1. Field of the Invention
The present invention relates generally to a four-cycle engine for an outboard motor and, more particularly, to an engine structure suitable for separation of oil in a PCV (positive crankcase ventilation) passage of a blow-by gas returning structure.
2. Description of the Related Art
An outboard motor employing a PCV system has been proposed in Japanese Patent Laid-Open Publication No. HEI-5-214921.
The proposed outboard motor has a crankcase and an intake tube communicating therewith through a hose so as to introduce a fresh air into the crankcase. In the outboard motor, a blow-by gas is supplied from a breather chamber provided sidewardly of a cylinder head to intake manifolds.
Since the cylinder head includes therein many lubricated parts such as cams, camshafts and valve rocker arms to which a lubricating oil is supplied, a large amount of oil mist is contained therein. Such an arrangement is not suitable for separating an oil from a blow-by gas within the breather chamber.
Apart from the related art described above, there is also proposed an outboard engine having a breather chamber disposed below a carburetor provided alongside the engine. However, since the breather chamber is positioned below the carburetor, the height of the breather chamber is restricted from extending vertically from an opening into which a blow-by gas flows. It is therefore difficult to obtain a breather chamber having a configuration suitable for separating an oil from a blow-by gas sufficiently, thereby requiring other breather chambers and an oil returning passage for returning an oil from the breather chamber to an oil pan. Thus, the engine is complicated in construction to thereby increase the number of parts thereof and hence the number of assembling steps, leading to increased coats of production.